Process of rapidly bleaching vegetable fibers of any kind



Patented Apr. 15, I930 UNITED STATES PATENT OFFICE CARL GUSTAV SCHWALBE, OF EBERSWALIJE, AND HERMANN WENZL, OF FRANKFOBT- ON-THE-MAIN, GERMANY, ASSIGNORS TO I. G. FARBENINDUSTRIE AKTIENGESELL- SCHAFT, OF FRANKFORT, GERMANY PROCESS OF RAPIDLY BLEACHING VEGETABLE FIBERS ANY KIND No Drawing. Application filed January 19, 1925,

This invention relates to a process of rapidly bleaching vegetable fibers of any kind,

whether they are loose or in a manufactured state. As is well known, one impregnates fibrous material with hypochlorite solutions and after complete impregnation removes the excess. of bleaching agent by mechanical means, whereby an aeration of the material to be bleached is obtained. However, hitherto in this process only diluted bleaching solutions of this kind have been employed, which usually contain hardly more than 1 gram chlorine per liter. Stronger hypochlorite solutions are generally considered to be 5 detrimental to the strength of the fibrous material, whether it may be in the form of single fibers or in a manufactured state.

Now we have found that an excellent bleaching effect without injuring the fibers may be obtained with highly concentrated hypochlorite solutions containing at least 10 grams of active chlorine, for instance 20 grams of active chlorine or more per liter.

For this purpose we may proceed in the following manner The material to be'bleached is wholly impregnated with the bleaching solution as in the above-mentioned process, and then the excess of the bleaching solution is immediately removed preferably by pressing, so that the remaining quantity of bleaching agent,owing to its high concentration, will be sufiicient to complete the bleaching process tothe desired extent (full or partial bleaching). The bleaching process applied tocraw cellulose (f. i. paper pulp from the'sulphite process) is in this case so rapidly eifected that owing to its short duration noinjury to the cellulosic material to be bleache'd is to be feared.

nated and expressed materialwith steam or a mixture of steam and air. Furthermorela little quantity of carbon" dioxide ma be added to the said air to reduce the alkalmity of the bleaching solution, whereby, as is generally known, the bleaching effect is acceler- This bleaching process isfurtheriacceler- Serial No. 3,449, and in- Germany J'uly 15, 192i.

ated. The saving of time with this process is considerable; on an average, one twentieth to one thirtieth of the time hitherto used for bleaching may suffice.

Instead of employing a press we may alsomake use of a suction-pump for removing the main part of the bleaching liquor and by carefully adding fresh water displace the last remnants of bleaching liquor. This addition of water may be carried out in similar manner as in the well-known displacing operation in the manufacture of nitrocellulose, that isto say the solution to be removed must be displaced in such a manner that dilution is avoided as far as possible.

In this way a considerably purer bleached material is obtained than with the usual process of bleaching and washing out in a rag-engine. In the bleaching liquor colloidal sub stances are dissolved. These are separated by diluting the concentrated bleaching'liquor with washing-Water. As we have shown by special experiments, a considerable quantity of colloidal substances is precipitated from an exhausted bleaching bath resulting from bleaching wood cellulose on diluting the said bath with an equal volume of water and after having been left standing. Therefore it is not advisable to remove the bleaching liquor as usual by diluting the pulp with washingwater, whereby the colloidal substances might be separated and preciptatcd upon the fiber which, as is well-known, exerts a strong adsorbing power on many substances, especially of colloidal nature.

The principles of the described rapidbleaching process may be applied to all kinds of vegetable fibers whether loose or manufactured; in the latter case with corresponding adaption of the operations as described in our copending application -Ser. No. 30,618. In order to illustrate the scope of our invention we will now give the following example,

cellulose pasteboard, the breadth of pasteboard may be simultaneously moistened and preheated by steam, and thereupon impregnated with bleaching solution, that is to say thoroughly wetted with a solution containing about 30 grams of active chlorine per liter, and then the excess of the bleaching solution is immediately removed therefrom by pressing. The bleaching is then effected by bringing the impregnated pasteboard into a moist and warm atmosphere. As the pasteboards are softened by the impregnating or preheating operation, or when being the product of the wet section of a desiccating machine, are completely soft from the beginning, it is advisable, in order to avoid the breadth being torn, to support them on supporting members such as guiding rolls, belts or a Wire-netting with coarse meshes. The soft pasteboard breadth must be supported by these means to such an extent that it may bear a transport of, say, 5 minutes on an average, through a moist and warm chamber or other suitable room, and a further treatment if required.

After the bleaching process has been completed the breadth having been wetted by absorbing some water from the moist atmos phere is squeezed out if desired removed from the supporting member and passed to a unravelling machine Where it is reduced to fibers. The pulp produced is washed in the usual way and subjected to further treatment. When a wire-netting is used as supporting member it may be again conducted to the rollers in the form of an endless sieve on which the soft breadths are placed. If however a thorough washing of the material in the form of pulp is not needed or the form of the pasteboards is to. be preserved, the breadth may be rinsed With water and the remainders of the spent bleaching solution removed by pressing as far as required Whereupon the pasteboard breadth may be separated from its support and conveyed to a drying device in the usual manner.

We claim :."I Y

1. In the gm of bleaching vegetable fibers especially cellulosic'raw material the combination of the following steps: placing the fibers in the form. of dry paste-board on a continuously -'moving supporting member, moistening and-preheating the fibers, impregnating the fibers with a strong bleaching liquor containing. from 20'to 30 grams of active chlorine per "liter, immediately remov ing the excess of bleaching agent, passing the treated fibers'through a moist and warm atmosphere'so that the bleaching agent remaining in the fibers effects the'bleaching to the desired degree, and finally removing the remnants of the exhausted bleaching liquor by rinsing them with water, pressing off the water, separating the bleached paste-board from the supporting member and conveying it to a drying device. 1

2. In the art of bleaching vegetable fibers especially cellulosic raw material the combination of the following steps: placing the fibers in the form of dry paste-board on'an endless screen continuously moving on rollers, moistening and preheating the fibers, impregnating the fibers with a strong bleaching liquor containing from 20 to 30 grams of active chlorine per liter, immediately remov- 3. In the art of bleaching vegetable fibers especially cellulosic raw material the combination of the following steps: placing the fibers in the form of dry paste-board on a continuously moving supporting member, moistening and preheating the fibers by steam, impregnating the fibers with a strong bleaching liquor containing from 20 to 30 grams of active chlorine perliter, immediately removing the excess of bleaching agent, passing the treated fibers through a moist and warm atmosphere so that the bleaching agent remaining in the fibers effects the bleaching to the desired degree, and finally removing the remnants of the exhausted bleaching liquor by rinsing them with water, pressing off the Water, separating the bleached paste-board from the supporting member and conveying it to a drying device.

4. In the art of bleaching vegetable fibers especially cellulosic raw material the combination of the following steps: placing the fibers in the form of dry paste-board ona continuously moving supporting member, moistening and preheating the fibers, impregnating the fibers with a strong bleaching liquor containing from 20 to 30 grams of active chlorine per liter, immediately removing the excess of bleaching agent, subjecting the treated fibers to an atmosphere containing steam so that the bleaching agent remaining in the fibers effects the bleaching to the desired degree, and finally removing the remnants of the exhausted bleaching liquor by rinsing them with water, pressing off the Water, separating the bleached paste-board from the supporting member and conveying it to a drying device; l

5. In the art of bleaching vegetable fibers especially cellulosic raw material the combination of the followin steps: lacing the fibers in the form of y paste-board on a continuously moving supporting member, molstening and preheating the fibers, impregnating the fi ers with a strong bleaching liquor containing from 20 to 30 ams of active chlorine per liter, immediate y removing the excess of bleaching agent, subjecting the treated fibers to an atmosphere contamin steam and carbon dioxide so that the bleaching agent remainin inthe 'fibers effects the bleaching to the esired degree and finally removing the remnants of the ex- ,hausted bleaching liwllor by rinsing them with water, pressing 011: t e water, separating the bleached paste-board from the supporting member. and conveying it to a drying device. In testimony whereof we afiix our signatures.v

- HERMANN WENZL. CARL GUSTAV SCHWALBE. 

